We will analyze the generation and specificity of influenza virus-induced human cytotoxic T lymphocytes (CTL) and interferon gamma. Influenza specific CTL are required for recovery from influenza infection in the murine model. We have demonstrated that lymphocytes of humans produce gamma interferon during the generation of HLA-restricted influenza-specific T lymphocyte responses, and a significant correlation exists between the levels of gamma interferon induced and the CTL response. In the proposed studies we will define the influenza virus antigens responsible for human CTL responses and gamma interferon production. We recently demonstrated a subtype-specific CTL response to an antigenic site on the HA2 subunit in the murine system. This subtype-specific CTL response is broadly cross-reactive within the Hl subtype. In the proposed studies we will determine whether this epitope induces subtype-specific CTL responses from human lymphocytes and determine whether a similar subtype-specific CTL antigenic site is present in viruses of the H3 subtype. The molecule containing the subtype-specific CTL determinant renders murine target cells from H-2d mice susceptible to lysis by influenza specific CTL; however, cells of H-2b or H-2k mice which are susceptible to CTL lysis when infected with virus are not rendered susceptible to lysis by this molecule. We will determine in the murine system the requirements for MHC restrictions of this subtype-specific CTL determinant. Human CTL studies will be done to determine whether specific HLA haplotypes also interact differently with the subtype-specific determinant as recognized by viru-immune CTLs. Studies will be performed using human lymphocytes to determine the precursor frequency of influenza-induced cross-reactive and subtype-specific CTL responses in normal adults, and following vaccination or recent infection. The duration of these CTL responses which are thought to be associated with protection will be determined. The effect of immunization or infection on the production of interferon gamma produced by human T lymphocytes and on the number of human lymphocytes producing interferon gamma will be assessed. The results of these experiments should provide basic insights into our understanding of the specificity and roles of human influenza specific CTLs, and their immunoregulatory relationships with interferon gamma.